Atmospheric distillation of crude oil

Distillation of crude oil is typically performed either under atmospheric pressure and under a vacuum. Low boiling fractions usually vaporize below 400 °C at atmospheric pressure without cracking the hydrocarbon compounds. Therefore, all the low boiling fractions of crude oil are separated by atmospheric distillation. A crude distillation unit (CDU) consists of pre-flash distillation column. The petroleum products obtained from the distillation process are light, medium, and heavy naphtha, kerosene, diesel, and oil residue.

Atmospheric crude distillation unit

Crude oil obtained from the desalter at temperature of 250 °C–260 °C is further heated by a tube-still heater to a temperature of 350 °C–360 °C. The hot crude oil is then passed into a distillation column that allows the separation of the crude oil into different fractions depending on the difference in volatility. The pressure at the top is maintained at 1.2–1.5 atm[1] so that the distillation can be carried out at close to atmospheric pressure, and therefore it is known as atmospheric distillation column.[2]

The vapors from the top of the column are a mixture of hydrocarbon gases and naphtha, at a temperature of 120 °C–130 °C. The vapor stream associated with steam used at bottom of the column is condensed by the water cooler and the liquid collected in a vessel is known as reflux drum which is present at the top of the column. Some part of the liquid is returned to the top plate of the column as overhead reflux, and the remaining liquid is sent to a stabilizer column which separates gases from liquid naphtha. A few plates below the top plate, the kerosene is obtained as product at a temperature of 190 °C–200 °C. Part of this fraction is returned to the column after it is cooled by a heat exchanger. This cooled liquid is known as circulating reflux, and it is important to control the heat load in the column. The remaining crude oil is passed through a side stripper which uses steam to separate kerosene. The kerosene obtained is cooled and collected in a storage tank as raw kerosene, known as straight run kerosene that boils at a range of 140 °C–270 °C. A few plates below the kerosene draw plate, the diesel fraction is obtained at a temperature of 280 °C–300 °C. The diesel fraction is then cooled and stored. The top product from the atmospheric distillation column is a mixture of hydrocarbon gases, e.g., methane, ethane, propane, butane, and naphtha vapors. Residual oil present at the bottom of the column is known as reduced crude oil[3] (RCO). The temperature of the stream at the bottom is 340 °C–350 °C, which is below the cracking temperature of oil.[4]

Simulation helps in crude oil characterization so that thermodynamic and transport properties can be predicted.[5] Dynamic models help in examining the relationships that could not be found by experimental methods (Ellner & Guckenheimer, 2006). By using modeling and simulation software, 80% of the time can be saved rather than constructing an actual working model. Also it saves cost. Moreover, a model can provide more accurate study of the real system.[6]

See also


  1. ^ The standard atmosphere (symbol: atm) is a unit of pressure defined as 101325 Pa (1.01325 bar), equivalent to 760 mm Hg (torr), 29.92 in Hg and 14.696 psi.
  2. ^ Fundamentals of petroleum and petrochemical engineering by Uttam Rai choudhari. Publication CRC press, International Standard Book Number: 978-1-4398-5160-9 (Hardback) chapter 3, pp. 52–53
  3. ^ Glossary of Petroleum Industry Common Terms & Symbols, alphabet R
  4. ^ Fundamentals of petroleum and petrochemical engineering by Uttam Rai choudhari. Publication CRC press, International Standard Book Number: 978-1-4398-5160-9 (Hardback) chapter 3, pp. 52–53
  5. ^
  6. ^ chapter 2 page 16

External links

  • Fundamentals of petroleum and petrochemical engineering by Uttam Rai Choudhari. Publication CRC press, International Standard Book Number: 978-1-4398-5160-9 (Hardback) chapter 3, pp. 52–53

Distillation is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Distillation may result in essentially complete separation (nearly pure components), or it may be a partial separation that increases the concentration of selected components in the mixture. In either case, the process exploits differences in the volatility of the mixture's components. In industrial chemistry, distillation is a unit operation of practically universal importance, but it is a physical separation process, not a chemical reaction.

Distillation has many applications. For example:

Distillation of fermented products produces distilled beverages with a high alcohol content or separates out other fermentation products of commercial value.

Distillation is an effective and traditional method of desalination.

In the fossil fuel industry, oil stabilization is a form of partial distillation that reduces vapor pressure of crude oil, thereby making it safe for storage and transport as well as reducing the atmospheric emissions of volatile hydrocarbons. In midstream operations at oil refineries, distillation is a major class of operation for transforming crude oil into fuels and chemical feed stocks.

Cryogenic distillation leads to the separation of air into its components – notably oxygen, nitrogen, and argon – for industrial use.

In the field of industrial chemistry, large amounts of crude liquid products of chemical synthesis are distilled to separate them, either from other products, from impurities, or from unreacted starting materials.An installation used for distillation, especially of distilled beverages, is called a distillery. The distillation equipment at a distillery is a still.

Oil refinery

Oil refinery or petroleum refinery is an industrial process plant where crude oil is transformed and refined into more useful products such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, jet fuel and fuel oils. Petrochemicals feed stock like ethylene and propylene can also be produced directly by cracking crude oil without the need of using refined products of crude oil such as naphtha.Oil refineries are typically large, sprawling industrial complexes with extensive piping running throughout, carrying streams of fluids between large chemical processing units, such as distillation columns. In many ways, oil refineries use much of the technology of, and can be thought of, as types of chemical plants.

The crude oil feedstock has typically been processed by an oil production plant. There is usually an oil depot at or near an oil refinery for the storage of incoming crude oil feedstock as well as bulk liquid products.

Petroleum refineries are very large industrial complexes that involve many different processing units and auxiliary facilities such as utility units and storage tanks. Each refinery has its own unique arrangement and combination of refining processes largely determined by the refinery location, desired products and economic considerations.

An oil refinery is considered an essential part of the downstream side of the petroleum industry.

Some modern petroleum refineries process as much as 800,000 to 900,000 barrels (127,000 to 143,000 cubic meters) of crude oil per day.

According to the Oil and Gas Journal in the world a total of 636 refineries were operated on the 31 December 2014 for a total capacity of 87.75 million barrels (13,951,000 m3).

Jamnagar Refinery is the largest oil refinery, since 25 December 2008, with a processing capacity of 1.24 million barrels (197,000 m3). Located in Gujarat, India, it is owned by Reliance Industries.

Siraf refineries complex

The Siraf refineries complex is an Iranian oil refinery. It is located at the Siraf region of Bushehr province, between 13th and 19th phases of the South Pars gas field over an area of approximately 300 hectares.

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